Nowadays, in water supply networks, a wide range of regulating elements are available which allow adjusting the values of water flow rate and pressure, at different points in the network, with the aim of meeting the needs of users.
An example of this is the case of the regulating valves which are capable of causing a frictional loss pressure to maintain a constant pressure at the outlet regardless of the flow rate. These valves are generally used to reduce the pressure in certain parts of the network, which prevents breakages or decreases the level of leakages.
On numerous occasions it has been tried to use hydraulic turbines to replace said regulating valves and to achieve an electrical exploitation, the major drawback being the adjustment of the turbine to the flow rate values changing over time (since they depend on the users demand), further having to maintain a constant pressure at the outlet (pressure regulating valves) or at the inlet (pressure sustaining valves).
A typical case of this flow rate variability is constituted by urban potable water supply networks, in which the flow rate at nighttime is very low compared to the water demand at daytime consumption peaks.
The applicant knows the existence of numerous devices or means for adjusting the operation of a turbine depending on the circulating flow rate or pressure differential to be exploited. Such systems are usually mechanical and are present in high power turbines for hydroelectric exploitation. As an example of this, devices can be mentioned that are based on the orientation of the blades of the turbine, as it is the case with Kaplan turbines. These systems seek to maintain a high performance and a given rotation rate regardless of the flow rate to be processed by the turbine and pressure differential to be exploited, since they are usually equipped with synchronous generators that must rotate at a given speed to inject the energy into the grid.
These systems have the disadvantage of their high mechanical complexity, especially when they are to be installed in a micro-turbine for energy recovery in urban supply networks.
Similarly, the applicant knows the existence of hydraulic micro-turbines installable in supply networks which, however, do not have a suitable control system that allow them to adjust its operation to the required conditions of flow rate and pressure. Therefore, these turbines are not able to ensure a constant pressure at the outlet, but it depends on the circulating flow rate.
In an attempt to improve the hydraulic operation of these micro-turbines, assemblies have been carried out by placing a reducing valve at the outlet or a stopper at the inlet in order to thus achieve a level of constant pressure at the outlet regardless of the flow rate.
In this regard, it is noteworthy that although they achieve their objective hydraulically, they result very energy inefficient because they do not allow exploiting all the available pressure differential, part of which is lost by friction in the regulating valve, the stopper or any other mechanical element.
In turn, and for a completely opposed aspect of such systems, the applicant knows the so-called “regenerative braking systems” used in various fields of industry, which allow regulating the braking torque of a generator and therefore the generated electrical power.
Typically, such regenerative braking systems are connected to generators or servomotors of the brushless type.
Practical examples of this can be found in hybrid vehicles (which recover energy from braking to recharge batteries), in new generation elevators, in servomotors for braking of shafts, etc.